Multiple sclerosis (MS) is a progressive neurologic disorder that is likely to have an autoimmune basis. We have been testing the safety and efficacy of cladribine (2-CdA) as a treatment for MS. Other current treatments are unsatisfactory, with Beta Interferon and Copaxone having a partial effect on relapses in MS. We have completed treatment trials in chronic progressive MS (subproject #220) and have shown that cladribine, an immunosuppressive agent, retards the progression of the disease for two years or longer. A double-blind, placebo-controlled clinical trial of cladribine in relapsing remitting MS has just been completed. The results indicate marked suppression of MRI-enhancing brain lesions in the cladribine treated group and significant reduction in both severity and frequency of clinical relapses. There was no significant toxicity or side effects of subcutaneously administered cladribine at the doses used in this study.